1. Field of the Invention
The present invention relates to a surface acoustic wave apparatus and a communications equipment with the surface acoustic wave apparatus, in particular, a surface acoustic wave apparatus with face-down mounting configuration which has an excellent out-of-band attenuation characteristic. This surface acoustic wave apparatus forms circuit components such as a surface acoustic wave filter and a surface acoustic wave resonator. These circuit components are used for communications equipment such as mobile phones.
2. Description Of Related Art
In recent years, as high frequency applications and functional enhancement of the communications equipment have progressed, the demand for a surface acoustic wave filter having the excellent out-of-band attenuation characteristic has increasingly grown.
For example, as a surface acoustic wave filter for mobile phones in the band of 900 MHz, there is a demand for the surface acoustic wave filter having the excellent out-of-band attenuation characteristic in which out-of-band attenuation in the vicinity of a pass band and in the high frequency band of several GHz is increased.
In order to realize such an excellent out-of-band attenuation characteristic, for example, a double-mode surface acoustic wave resonator filter which is provided with three IDT (Inter Digital Transducer) electrodes on a piezoelectric substrate and uses a vertical primary mode and a vertical tertiary mode has been proposed.
FIG. 16 is a schematic plan view showing the configuration of electrodes in a conventional resonator-type surface acoustic wave filter.
An IDT electrode 204 having a plurality of electrode fingers arranged on the piezoelectric substrate is formed of a pair of comb-like electrodes which are opposed to and engaged with each other, and an electric field is applied to the pair of comb-like electrodes, thereby generating a surface acoustic wave.
By inputting an electric signal from an input terminal 215 connected to one comb-like electrode of the IDT electrode 204, the excited surface acoustic wave is propagated to IDT electrodes 203 and 205 arranged at both sides of the IDT electrode 204.
The electric signal is output from one comb-like electrode forming the IDT electrodes 203 and 205, respectively, to output terminals 216 and 217 through IDT electrodes 206 and 209. Reference numerals 210, 211, 212 and 213 in this figure each denote a reflector electrode.
Here, by inputting the electric signal to an input terminal 215, the surface acoustic wave is excited, and the excited surface acoustic wave is propagated to the IDT electrodes 203 and 205 located at both sides of the IDT electrode 204 and to IDT electrodes 207 and 208 sandwiched between the IDT electrode 206 and 209 through the IDT electrodes 206 and 209. Then, the electric signal is output from the output terminals 216 and 217 connected to the IDT electrodes 207 and 208. The surface acoustic wave is reflected by the reflector electrodes 210, 211, 212 and 213 located at both ends and becomes a standing wave between the reflector electrodes 210 and 211 and between the reflector electrodes 212 and 213.
With the above-mentioned two-stage cascade connection of the surface acoustic wave filter having the similar characteristic, the signal attenuated at the first stage can be further attenuated by the second stage, thereby increasing the out-of-band attenuation by about 100%.
To realize the excellent out-of-band attenuation characteristic and reduce insertion loss, the number of stages of the surface acoustic wave filter is preferably two as shown in FIG. 16. In the case of one stage, although insertion loss is small, the out-of-band attenuation is decreased. Conversely, in the case of three or more stages, although the out-of-band attenuation is increased, insertion loss is increased.
Conventionally, the surface acoustic wave device in which such a surface acoustic wave filter is formed is mounted on a package by a face-up mounting method. In this case, by electrically connecting the surface acoustic wave filter to a ground electrode of the package with the use of a bonding wire, a large inductance can be added between the surface acoustic wave filter and the ground electrode, rise of the floor level outside the pass band of the surface acoustic wave filter can be prevented, and the out-of-band attenuation characteristic can be further improved.
On the other hand, to further miniaturize the surface acoustic wave apparatus, a CSP (Chip Scale Package)-type surface acoustic wave apparatus using so-called flip-chip mounting technology in which a conductor bump is used to mount the surface acoustic wave device by the face-down mounting method has been actively developed (refer to Japanese Unexamined Patent Publication No. 2000-49565).
FIG. 17 is a schematic sectional view of the conventional CSP-type surface acoustic wave apparatus.
FIG. 17 shows a piezoelectric substrate 51, a ground pad 52 formed on a bottom face of the piezoelectric substrate 51, an IDT electrode 53 formed on the bottom face of the piezoelectric substrate 51, a ground electrode 54 formed at a package 57, a bump 55 which connects the ground pad 52 to the ground electrode 54, a lid 56 which covers a recessed portion of the package 57 from above and hermetically seals the surface acoustic wave device within the package 57, and a connection layer 58 which connects the package 57 to the lid 56.
As described above, the CSP-type surface acoustic wave apparatus has been developed to improve the out-of-band attenuation characteristic while achieving miniaturization. However, when the CPS-type surface acoustic wave apparatus is produced for the miniaturization of communications equipment, a bonding wire used in the conventional face-up type surface acoustic wave apparatus cannot be used. For this reason, a large inductance cannot be added between the surface acoustic wave filter and the ground electrode (when the inductance is small, an attenuation pole is located at the side of high frequency and thus the attenuation pole cannot contribute to improvement in the filter characteristic) Therefore, there is a problem that the floor level outside the pass band of the surface acoustic wave filter rises and out-of-band attenuation becomes insufficient.
Moreover, the surface acoustic wave apparatus shown in FIG. 17 has the configuration in which the surface acoustic wave device is contained in the package 57 and the top face of the package 57 is hermetically sealed with the lid 56 to prevent oxidization of the IDT electrode 53 and the like. This configuration is disadvantageous to further reduce of the surface acoustic wave apparatus in size and height.
An object of the present invention is to provide a surface acoustic wave apparatus with face-down mounting configuration which is excellent in out-of-band attenuation characteristic and can be reduced in size and height and a communications equipment using the surface acoustic wave apparatus.